Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $47.34   7.340%   $50.8148   $50.81   $50.80   $50.80  
  Purchase #2 $11.63   11.647%   $12.9845   $12.98   $13.00   $13.00  
  Purchase #3 $33.56   9.523%   $36.7559   $36.76   $36.75   $36.80  
  Purchase #4 $61.92   11.728%   $69.182   $69.18   $69.20   $69.20  
  Purchase #5 $8.72   4.652%   $9.1257   $9.13   $9.15   $9.10  
  Purchase #6 $87.59   4.217%   $91.2837   $91.28   $91.30   $91.30  
  Purchase #7 $179.72   5.358%   $189.3494   $189.35   $189.35   $189.30  
  7 purchase totals = $430.48       $459.4960   $459.49   $459.55   $459.50